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 * Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.io;

/**
 * This abstract class is the superclass of all classes representing an input
 * stream of bytes.
 *
 * <p>
 * Applications that need to define a subclass of <code>InputStream</code> must
 * always provide a method that returns the next byte of input.
 *
 * @author Arthur van Hoff
 * @version 12/17/01 (CLDC 1.1)
 * @see java.io.ByteArrayInputStream
 * @see java.io.DataInputStream
 * @see java.io.InputStream#read()
 * @see java.io.OutputStream
 * @since JDK1.0, CLDC 1.0
 */
public abstract class InputStream implements Closeable {

    /**
     * Reads the next byte of data from the input stream. The value byte is
     * returned as an <code>int</code> in the range <code>0</code> to
     * <code>255</code>. If no byte is available because the end of the stream
     * has been reached, the value <code>-1</code> is returned. This method
     * blocks until input data is available, the end of the stream is detected,
     * or an exception is thrown.
     *
     * <p>
     * A subclass must provide an implementation of this method.
     *
     * @return the next byte of data, or <code>-1</code> if the end of the
     * stream is reached.
     * @exception IOException if an I/O error occurs.
     */
    public abstract int read() throws IOException;

    /**
     * Reads some number of bytes from the input stream and stores them into the
     * buffer array <code>b</code>. The number of bytes actually read is
     * returned as an integer. This method blocks until input data is available,
     * end of file is detected, or an exception is thrown.
     *
     * <p>
     * If <code>b</code> is <code>null</code>, a
     * <code>NullPointerException</code> is thrown. If the length of
     * <code>b</code> is zero, then no bytes are read and <code>0</code> is
     * returned; otherwise, there is an attempt to read at least one byte. If no
     * byte is available because the stream is at end of file, the value
     * <code>-1</code> is returned; otherwise, at least one byte is read and
     * stored into <code>b</code>.
     *
     * <p>
     * The first byte read is stored into element <code>b[0]</code>, the next
     * one into <code>b[1]</code>, and so on. The number of bytes read is, at
     * most, equal to the length of <code>b</code>. Let <i>k</i> be the number
     * of bytes actually read; these bytes will be stored in elements
     * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
     * leaving elements <code>b[</code><i>k</i><code>]</code> through
     * <code>b[b.length-1]</code> unaffected.
     *
     * <p>
     * If the first byte cannot be read for any reason other than end of file,
     * then an <code>IOException</code> is thrown. In particular, an
     * <code>IOException</code> is thrown if the input stream has been closed.
     *
     * <p>
     * The <code>read(b)</code> method for class <code>InputStream</code> has
     * the same effect as:
     * <pre><code> read(b, 0, b.length) </code></pre>
     *
     * @param b the buffer into which the data is read.
     * @return the total number of bytes read into the buffer, or
     * <code>-1</code> is there is no more data because the end of the stream
     * has been reached.
     * @exception IOException if an I/O error occurs.
     * @see java.io.InputStream#read(byte[], int, int)
     */
    public int read(byte b[]) throws IOException {
        return read(b, 0, b.length);
    }

    /**
     * Reads up to <code>len</code> bytes of data from the input stream into an
     * array of bytes. An attempt is made to read as many as <code>len</code>
     * bytes, but a smaller number may be read, possibly zero. The number of
     * bytes actually read is returned as an integer.
     *
     * <p>
     * This method blocks until input data is available, end of file is
     * detected, or an exception is thrown.
     *
     * <p>
     * If <code>b</code> is <code>null</code>, a
     * <code>NullPointerException</code> is thrown.
     *
     * <p>
     * If <code>off</code> is negative, or <code>len</code> is negative, or
     * <code>off+len</code> is greater than the length of the array
     * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is thrown.
     *
     * <p>
     * If <code>len</code> is zero, then no bytes are read and <code>0</code> is
     * returned; otherwise, there is an attempt to read at least one byte. If no
     * byte is available because the stream is at end of file, the value
     * <code>-1</code> is returned; otherwise, at least one byte is read and
     * stored into <code>b</code>.
     *
     * <p>
     * The first byte read is stored into element <code>b[off]</code>, the next
     * one into <code>b[off+1]</code>, and so on. The number of bytes read is,
     * at most, equal to <code>len</code>. Let <i>k</i> be the number of bytes
     * actually read; these bytes will be stored in elements <code>b[off]</code>
     * through <code>b[off+</code><i>k</i><code>-1]</code>, leaving elements
     * <code>b[off+</code><i>k</i><code>]</code> through
     * <code>b[off+len-1]</code> unaffected.
     *
     * <p>
     * In every case, elements <code>b[0]</code> through <code>b[off]</code> and
     * elements <code>b[off+len]</code> through <code>b[b.length-1]</code> are
     * unaffected.
     *
     * <p>
     * If the first byte cannot be read for any reason other than end of file,
     * then an <code>IOException</code> is thrown. In particular, an
     * <code>IOException</code> is thrown if the input stream has been closed.
     *
     * <p>
     * The <code>read(b,</code> <code>off,</code> <code>len)</code> method for
     * class <code>InputStream</code> simply calls the method
     * <code>read()</code> repeatedly. If the first such call results in an
     * <code>IOException</code>, that exception is returned from the call to the
     * <code>read(b,</code> <code>off,</code> <code>len)</code> method. If any
     * subsequent call to <code>read()</code> results in a
     * <code>IOException</code>, the exception is caught and treated as if it
     * were end of file; the bytes read up to that point are stored into
     * <code>b</code> and the number of bytes read before the exception occurred
     * is returned. Subclasses are encouraged to provide a more efficient
     * implementation of this method.
     *
     * @param b the buffer into which the data is read.
     * @param off the start offset in array <code>b</code> at which the data is
     * written.
     * @param len the maximum number of bytes to read.
     * @return the total number of bytes read into the buffer, or
     * <code>-1</code> if there is no more data because the end of the stream
     * has been reached.
     * @exception IOException if an I/O error occurs.
     * @see java.io.InputStream#read()
     */
    public int read(byte b[], int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0)
                || ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }

        int c = read();
        if (c == -1) {
            return -1;
        }
        b[off] = (byte) c;

        int i = 1;
        try {
            for (; i < len; i++) {
                c = read();
                if (c == -1) {
                    break;
                }
                if (b != null) {
                    b[off + i] = (byte) c;
                }
            }
        } catch (IOException ee) {
        }
        return i;
    }

    /**
     * Skips over and discards <code>n</code> bytes of data from this input
     * stream. The <code>skip</code> method may, for a variety of reasons, end
     * up skipping over some smaller number of bytes, possibly <code>0</code>.
     * This may result from any of a number of conditions; reaching end of file
     * before <code>n</code> bytes have been skipped is only one possibility.
     * The actual number of bytes skipped is returned. If <code>n</code> is
     * negative, no bytes are skipped.
     *
     * <p>
     * The <code>skip</code> method of <code>InputStream</code> creates a byte
     * array and then repeatedly reads into it until <code>n</code> bytes have
     * been read or the end of the stream has been reached. Subclasses are
     * encouraged to provide a more efficient implementation of this method.
     *
     * @param n the number of bytes to be skipped.
     * @return the actual number of bytes skipped.
     * @exception IOException if an I/O error occurs.
     */
    public long skip(long n) throws IOException {
        long m = n;
        while (m > 0) {
            if (read() < 0) {
                break;
            }
            --m;
        }
        return n - m;
    }

    /**
     * Returns the number of bytes that can be read (or skipped over) from this
     * input stream without blocking by the next caller of a method for this
     * input stream. The next caller might be the same thread or another thread.
     *
     * <p>
     * The <code>available</code> method for class <code>InputStream</code>
     * always returns <code>0</code>.
     *
     * <p>
     * This method should be overridden by subclasses.
     *
     * @return the number of bytes that can be read from this input stream
     * without blocking.
     * @exception IOException if an I/O error occurs.
     */
    public int available() throws IOException {
        return 0;
    }

    /**
     * Closes this input stream and releases any system resources associated
     * with the stream.
     *
     * <p>
     * The <code>close</code> method of <code>InputStream</code> does nothing.
     *
     * @exception IOException if an I/O error occurs.
     */
    public void close() throws IOException {
    }

    /**
     * Marks the current position in this input stream. A subsequent call to the
     * <code>reset</code> method repositions this stream at the last marked
     * position so that subsequent reads re-read the same bytes.
     *
     * <p>
     * The <code>readlimit</code> arguments tells this input stream to allow
     * that many bytes to be read before the mark position gets invalidated.
     *
     * <p>
     * The general contract of <code>mark</code> is that, if the method
     * <code>markSupported</code> returns <code>true</code>, the stream somehow
     * remembers all the bytes read after the call to <code>mark</code> and
     * stands ready to supply those same bytes again if and whenever the method
     * <code>reset</code> is called. However, the stream is not required to
     * remember any data at all if more than <code>readlimit</code> bytes are
     * read from the stream before <code>reset</code> is called.
     *
     * <p>
     * The <code>mark</code> method of <code>InputStream</code> does nothing.
     *
     * @param readlimit the maximum limit of bytes that can be read before the
     * mark position becomes invalid.
     * @see java.io.InputStream#reset()
     */
    public synchronized void mark(int readlimit) {
    }

    /**
     * Repositions this stream to the position at the time the <code>mark</code>
     * method was last called on this input stream.
     *
     * <p>
     * The general contract of <code>reset</code> is:
     *
     * <p>
     * <ul>
     *
     * <li> If the method <code>markSupported</code> returns <code>true</code>,
     * then:
     *
     * <ul><li> If the method <code>mark</code> has not been called since the
     * stream was created, or the number of bytes read from the stream since
     * <code>mark</code> was last called is larger than the argument to
     * <code>mark</code> at that last call, then an <code>IOException</code>
     * might be thrown.
     *
     * <li> If such an <code>IOException</code> is not thrown, then the stream
     * is reset to a state such that all the bytes read since the most recent
     * call to <code>mark</code> (or since the start of the file, if
     * <code>mark</code> has not been called) will be resupplied to subsequent
     * callers of the <code>read</code> method, followed by any bytes that
     * otherwise would have been the next input data as of the time of the call
     * to <code>reset</code>. </ul>
     *
     * <li> If the method <code>markSupported</code> returns <code>false</code>,
     * then:
     *
     * <ul><li> The call to <code>reset</code> may throw an
     * <code>IOException</code>.
     *
     * <li> If an <code>IOException</code> is not thrown, then the stream is
     * reset to a fixed state that depends on the particular type of the input
     * stream and how it was created. The bytes that will be supplied to
     * subsequent callers of the <code>read</code> method depend on the
     * particular type of the input stream. </ul></ul>
     *
     * <p>
     * The method <code>reset</code> for class <code>InputStream</code> does
     * nothing and always throws an <code>IOException</code>.
     *
     * @exception IOException if this stream has not been marked or if the mark
     * has been invalidated.
     * @see java.io.InputStream#mark(int)
     * @see java.io.IOException
     */
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }

    /**
     * Tests if this input stream supports the <code>mark</code> and
     * <code>reset</code> methods. The <code>markSupported</code> method of
     * <code>InputStream</code> returns <code>false</code>.
     *
     * @return  <code>true</code> if this true type supports the mark and reset
     * method; <code>false</code> otherwise.
     * @see java.io.InputStream#mark(int)
     * @see java.io.InputStream#reset()
     */
    public boolean markSupported() {
        return false;
    }

}
